1. Field of the Invention
The present invention relates to the structure of a photoelectric conversion region in a photoelectric conversion device.
2. Description of the Related Art
As a photoelectric conversion region of each pixel of a photoelectric conversion device, a configuration in which a photodiode formed by PN junction between first and second conductivity-type semiconductor regions is included and in which an interlayer insulating film formed of a silicon oxide film or the like is arranged on the photodiode is known. The interlayer insulating film may have a protective insulating film, a color filter, or the like provided thereon, or may be in direct contact with air. A photoelectric conversion device having such a structure often exhibits, as the spectral characteristics thereof, characteristics in which an output has ripple in relation to the wavelength of incident light. Ripple occurs when the incident light undergoes multiple reflections at the interfaces between the photoelectric conversion region and the interlayer insulating film and between the interlayer insulating film and a film that is formed on the interlayer insulating film and has a refractive index different from that of the interlayer insulating film. More specifically, ripple occurs due to the film thickness distribution of the interlayer insulating film in a chip, which causes variation in the effect of the multiple reflections between the positions of the pixels arranged on the chip.
In order to reduce ripple, as described in Japanese Patent Laid-Open No. 6-125068, there is a scheme for reducing ripple by randomizing the effect of optical interference using a structure in which a foundation pattern is attached to an insulating film to vary the height of the surface of the insulating film and another structure in which an island-shaped metal layer is provided on the insulating film.
In addition, in Japanese Patent Laid-Open No. 2005-072097, there is disclosed a photoelectric conversion device in which recesses and projections are formed in the surface of a semiconductor substrate by etching in order to reduce reflection at the interface on the lower side of an insulating film.
In the case of the former structure disclosed in Japanese Patent Laid-Open No. 6-125068, however, since the shape of the surface of the protective insulating film is different depending on the position, the protection property may be affected. In addition, since the thickness of the protective insulating film itself varies depending on the position, the protection property is different for each position on a chip, which may not be desirable. Furthermore, in the case of the island-shaped metal layer being provided (in the case of the latter structure disclosed in Japanese Patent Laid-Open No. 6-125068), an aperture in the photoelectric conversion region is smaller, which may also not be desirable.
As to Japanese Patent Laid-Open No. 2005-072097, the specific sizes of the recesses and projections are not described clearly. The effect of ripple may not be reduced depending on the sizes of the recesses and projections.